Cracking of hydrocarbon oils



Feb. 2, 1937. J. D. sx-:GUY

CRACKING OF HYDROCARBON OILS Original Filed Feb. 8, 1930 Feb. 2, 1937.J, D, SEGUY 2,069,392

4CRACKING OF HYDROCARBON OILS Original Filed Feb. 8, 1930 2 Sheets-Sheet2 Fleta /NVENTOR @y mw@ I@ Patented Feb. 2, 1931 UNITED STATES PATENT4OFFICE CRACKING OF HYDRCARBON OILS Ware Application February 8, 1930,Serial No. 426,805 Renewed September 20, 1934 1 Claim.

In so-called liquid-phase or low temperature cracking processes whereinhydrocarbon oils are subjected to conversion temperatures undersuperatmospheric pressures in a coil and enlarged 5 reaction zone inwhich the vaporized and unvaporized products are separated, the vaporssubjectecl to fractionation to eifect separation of the desired lightproducts from the heavier insufflciently converted portions, and theseheavier insufficiently converted products returned as reflux condensateto the heating coil for retreatment, it is known that this refluxcondensate is ordinarily lighter and more refractory to crackingreaction than the raw oil charged to the process.

This reflux will thus require more prolonged or more severe treatmentthan that to which the raw oil is best suited and, in the system men-ytioned wherein this reflux is returned to the heating coil forreconversion under the same conditions as those to which 'the raw oil issubjected, two undesirable conditions may arise; either the conversionconditions are so severe that overdecomposition of the raw oil (with aresulting high coke and gas formation) l may occur or the conversionconditions are too mild for the Aproper reconversion of the reflux,necessitating repeated recycling of this product, the ratio of reflux toraw oil sometimes running as high as five to one, or even higher, thusimposing an excessive load on the furnace and other parts of theapparatus.

It has been proposed to subject this refractory reflux condensate toreconversion in a separate heating zone under conditions of temperature.pressure and time better suited for the production of a maximum yield ofmotor fuel therefrom. 'I'he conditions of reconversion employed areoften of the higher order known as high temperature, or so-calledvapor-phase cracking.

The fact that 'reflux condensate from the frac- 40 tionating zone of aso-called vapor-phase or high temperature cracking process handlingrefractory charging stock may be, under some conditions.,

heavier and/or less refractory to cracking than the charging stock tothis process does not seem to be recognized.

It is among the purposes of this invention to provide an improved systemof cracking' employing respectively relatively mild and relativelysevere conversion conditions, subjecting the more refractoryhydrocarbons to the relatively severe conversion conditions best suitedto the desired degree of their decomposition and subjecting the lessrefractory products to reconversion under the relatively mild conditionsbest suited for the desired degree of their decomposition.

(Ol. 19H0) One method of realizing the purposes of my invention may beto nrst subject a relatively refractory charging stock to conditionscommonly known as vapor-phase or high temperature cracking. Theseconditions may comprise heat- 5 ing the oil to temperatures of the orderof 1000 to 1200 F., more or less, under relatively low pressure whichmay range from atmosphericQ pressure to a few hundred pounds per squareinch. The heated mass may be discharged into 10 an enlarged zone whereany unvaporized products such as carbon and heavy coke-like or pitchymaterials are precipitated and separated from the vapors, the latterpassing from this separating zone into a fractionating zone. 15

Well known means of cooling and fractionation may be employed in thefractionating zone, the

desired light products (which may consist of material boiling within therange 'of motor fuel) being condensed, cooled and collected after leav-20 ing the fractionating zone and the heavier portions of the vapors notboiling within the required range of motor fuel being cooled andcondensed in the'fractionating zone and collected as reflux condensatefrom the so-called vapor-phase sys- 25 tem. This reflux condensate maybe heavier and less refractory to cracking conditions than the oil usedas charging stock to the vapor-phase or relatively high temperatureheating element and may be fed to another heating element employing 30milder conversion conditions such as are commonly employed in /so-calledliquid-phase cracking systems. These milder conditions may comprisesubjecting the oil to reconversion at temperatures between 800 F. and950 F., more or 35 less, and under pressures of say to 1500 pounds persquare inch, more or less. The reconverted products leaving the lowtemperature heating element may be introduced into an enlarged reactionzone wherein separation of the vaporized and 40 unvaporized productsoccurs.

The vapors from this reaction zone may be removed and subjected tofractionation, the desired light products from the fractionating zonebeing separately cooled, condensed and collected 45 and the heavierinsufficiently converted products from the fractionating zone beingreturned as reflux condensate to either the low temperature or the-hightemperature heating element, depending on their composition and theconditions best 50 suited for their desired reconversion. Theunvaporized products from the reaction chamber of the low temperaturesystem may be withdrawn from the system or may be subjected to a furthervaporization of their lighter portions in 55 a zone of substantiallyreduced pressure. The unvaporized products from this zone of reducedpressure may be withdrawn from the system and the vaporized products maybel subjected to fractionation. The lighter portions of these dashedvapors may leave'the fractionating zone to be condensed, cooled andcollected as flash distillate; the heavier portions of the flashedvapors may be condensed as reflux condensate from the flashing part ofthe system. Either or both the flash distillate and reflux condensatefrom the flashing system may be returned to either the high temperatureor the low temperature heating zone, depending upon which conditions arebest suited for their desired reconversion.

It will be understood that any of the intermediate products from theprocesssuch as reflux condensate lfrom the high temperature system,reilux condensate from the low temperature system, reux condensate fromthe flashing system, residual or unvaporized products from the reactionzone of the low temperature system and flash distillate may be isolatedwholly or in part from the process as desired. It will be alsounderstood that any of the well known means of cooling and assistingfractionation may be employed in any and in all of the variousfractionating zones and that substantially uniform, reduced or increasedpressures of a wide range may be employed betwen the various componentparts of the process. It will also be understood that well known meansfor controlling the reaction in the various elements of the system maybe used such as cooling the oil discharging from the heating coils or inthe reaction zones to the proper temperature.

Many salient features not enumerated will be apparent from theforegoing, general description of one embodiment of my improved process.

In the attached drawings, Figs. 1 and 2 com prise a diagrammatic view inelevation, not to scale, of one of the many types of apparatus in whichmy process may be carried out.

Referring more in detail to the drawings, raw oil charging stock,introduced through line I and valve 2 to pump 3, may be fed through line4 and valve 5 into the high temperature heating element 8 which islocated in a suitable furnace setting 1 and after being brought to thedesired outlet temperature the heated mass may pass through line 8 andvalve 9 into reaction chamber I8. In chamber Ill the carbon and otherundesirable solid, semi-solid or liquid products are separated from thevapors and removed from the chamber through line II, controlled by valveI2. lIhe vapors from chamber III may pass through line |3 and valve |4into the fractionating zone Il. Any suitable cooling medium such asdistillate from the process may be introduced through line I6 and valveI1 into the fractionating zone I5 to assist fractionation therein. Bymaintaining the proper outlet temperature, at the top of fractionatingtower I5 only the desired light products, which may be those fallingwithin the boiling range of motor fuel, will remain as vapors at the topof this fractionating tower, and these vapors may be removed throughline I8 and valve I9, condensed and cooled in condenser 2l and, afterpassing through line 2| and valve 22, collected in receiver 23.Uncondensed gas may be withdrawn from receiver 23 through line 24,controlled by valve 25 and the condensed distillate may be withdrawnthrough line 26, controlled by valve 21.

Reiiux condensate from the fractionating tower Il is temporarilycollected in the bottom of this fractionating tower and may. be fed asdesired through line 23, valve 23, pump 38, line 3|, valve 32 and line33 to the low temperature heating element 34 which is located in asuitable furnace setting 35. The heated and reconverted products fromthe heating element 34 may pass through transfer line 38 and valve 31into the reaction chamber 38. A separation occursI in reaction chamber38 between the vaporized and unvaporized products, said vapors beingremoved through line 39 and valve 40 to the fractionating tower 4|. Inthis fractionating tower a suitable cooling medium may be employedeither in direct or in indirect contact with the ascending vapors toassist their fractionation, and this cooling medium may be introducedthrough line 42,' controlled by valve 42'. Vapors of the desired boilingrange are withdrawn from the fractionating tower 4| through line 43 andvalve 44 and, after being cooled and condensed in condenser 45, may passthrough line 46 and valve 41 into the receiver 48 from which uncondensedgas may be withdrawn through valve 49 and line 50. The distillate fromthis receiver may be withdrawn through valve 5| and line 52.

Reflux condensate from the fractionating tower 4| of the low temperaturesystem may be returned through line 53, valve 54, pump 55, line 58,valve 51, line 58 and line 4 to the high-temperature heating element 6for reconversion. All or a portion of this product may, however, when sodesired, be diverted from line 56 through line 58 and valve 60 into line33 from which it may be supplied to the low-temperature heating element34 for reconversion.

Unvaporized residual products from reaction chamber 38 of thelow-temperature systeznmay be withdrawn through line 6| and valve 82 andmay be either withdrawn from the system through valve 63 or may passthrough line 64 and valve 65 into the flash chamber 6G. The pressure onthe hot residual product is reduced in passing through valve 65 and thelatent heat liberated by this pressure reduction will serve to vaporizelight portions of the residual oil introduced into the flash chamber 85.The unvaporized nal residual product from this flash. chamber may bewithdrawn from the system through line 81 and valve 88. The vapors fromflash chamber 66 may pass through line 69 and valve 10 into the dashdephlegmator 1| where the desired light portions of the vapors areseparated from the heavier portions, the separation being assisted, ifdesired, by a cooling medium introduced through line 12 and valve 13.

That portion of the flash vapors remaining uncondensed at thetemperature maintained at the top of flash dephlegmator 1| may bewithdrawn therefrom through line 14 vand valve 15 and, after beingrcondensed and cooled in condenser 16, pass through line 11 and valve 18into the receiver 19. Uncondensed gases may be withdrawn from receiver19 through line 80. controlled by valve 8| and the condensed distillatemay be withdrawn through line 82, controlled by valve 83. A portion orall of this distillate may, if desired, be returned by means of line 84,valve 85, pump 88, line 81, valve 88, line 58 and line 4, to thehigh-temperature heating element 6 for reconversion. Any portion or allof this recycled material may, at will, be diverted from line 81 throughline 89, valve 90 and line 33 for reprocessing in the low temperatureheating element 34. The reflux condensate from flash dephlegmator 1I iswithdrawn therefrom through line 9| and valve 92 and may be fed by meansof pump 93 through line 94, valve 95, line 58 and line 4 to undergoreconversion in the high temperature heating element 6. A portion or allof this product may likewise be diverted from line 94 as desired and bypassing through line 96, valve 91 and line 33 may be fed to the lowtemperature heating element 34 for reconversion therein. Any portion orall of this reflux condensate from the flash dephlegmator may be fedoverhead to the fractionating tower 4I through line 98, controlled byvalve 99, or it may be fed overhead to the fractionating tower I5through line |00, controlled by valve IUI. By feeding this materialoverhead either to fractionating tower I5 or to fractionating tower 4I,or in part to both, all but its lightest portions will eventually bereturned through the pumps 3l! and/or 55 to either the high temperatureheating element 6 or to the low temperature heating element 34, as thecase may be, or if fed in part to both fractionating towers the productwill be reconverted in a like proportion in the high-temperature heatingelement 6 and the low-temperature heating element 34, respectively.

As a specific example of one particular operation incorporating mymethod of cracking as carried out in the above described process, a 32A. P. I. gravity intermediate product, commonly known as pressuredistillate bottoms, produced, for instance, from a separate so-calledliquidphase cracking process, or from any other source, may be fed tothe high-temperature or so-called vapor-phase heating element 6, inwhich it may be heated under a pressure of about fifty pounds per squareinch to a nal temperature of about 1100 F. A small portion of heavypitchy material may be withdrawn from the bottom of separating chamber Iwhich is also maintained under a pressure of approxim-ately fty poundsper square inch. The temperature at the top of fractionating tower I maybe maintained at about 350 F. by recirculating a portion of the productfrom receiver 48 to control cooling. The vaporphase cracked productcollected from receiver 23 will thus fall within the boiling range ofmotor fuel and may amount to approximately 25% of the raw oil charged tothe process.

The reilux condensate from the fractionating tower I5 may be fed throughthe low-temperature heating element 34 maintained at a pressure ofapproximately 150 pounds per square inch, and ma" be heated in this coilto an outlet temperature of approximately 850 F. The reaction chamber 38may also be held at about .this same pressure, but in this case thepressure in the fractionating tower 4I may be reduced to approximatelyflfty pounds per square inch by the control of valve 40. Vaporswithdrawn from the top of fractionating tower 4I may be at a temperatureof about 350 F. and the distillate collected in receiver 48 will thusmeet the boiling range requirements :forA commercial motor fuel and thisproduct may amount to approximately 45% based on the raw oil.

Residual oil may be withdrawn from the reaction chamber 38 and ied intothe flash chamber 66 at a reduced pressure of approximately thirtypounds per square inch. Substantially this same pressure may bemaintained on the flash dephlegmator 1I and the distillate removed fromthis dephlegmator and collected in receiver I9 may be returned to thedephlegmator 4I through line 42 and valve 42 to assist cooling thereinand after combining with the reflux condensate from this dephlegmatormay be fed by means of pump 55 back to the high temperature heatingelement 6 where the combined product may undergo reconversion togetherwith the charging stock. A portion of the flash distillate from thereceiver 'I9 may be recirculated through line I2 and valve 'I3 to thetop of the flash dephlegmator 1I to control cooling in this zone and thereflux condensate from dephlegmator 1I may be returned to the lowtemperature heating element 34, there to undergo reconversion, togetherwith the reflux condensate from the fractionating tower I5.

The flnal residual liquid formed in flash chamber 66 may amount to about12% of the raw oil and may be removed from the system through line 61.

It is evident from the foregoing that by the use of my improved processit is possible to convert a relatively refractory charging stock with areduced coke and gas formation and with consequently lower processlosses than are ordinarily experienced in the vapor-phase cracking ofoil of this character. It will also be noted that a higher yield ofmotor fuel is obtainable from this process than could be obtained by avapor-phase conversion alone and in many instances this product will beof a much more stable nature than the usual run of vapor-phase cracked.distillate, and yet have an anti-knock rating comparable with the highrating characteristic of a product made b y the vapor-phase method, atthe same time the gas loss may be materially decreased by the use of myprocess.

It is to be noted that the process is not limited to .the treatment ofso-called pressure distillate bottoms, but other suitable chargingstocks may be treated according tothe process of my invention.

I claim as my invention:

A process for producing gasoline from hydrocarbon charging oil which isrelatively light and refractory to cracking, said process comprisingsubjecting such charging oil while substantially in the vapor phase tocracking treatment at a temperature in excess of 1000 F. and convertingthe same into a vaporous mixture containing gasoline-like hydrocarbonsand hydrocarbons of higher boiling point than said charging oil,dephlegmating said vaporous mixture and condensing therefrom thehydrocarbons which are of higher boiling point than the charging oil,subjecting resultant condensate to a cracking treatment at lowertemperature than that of the first-mentioned cracking treatment, whileunder suillcient pressure to maintain a substantial portion thereof inthe liquid phase, separating the reaction products of the last-namedcracking treatment into vapors and unvaporized oil, recoveringgasoline-like hydrocarbons from said vapors, flash distilling saidunvaporized oil by pressure reduction and dephlegmating the flashedvapors independently of said vaporous mixture, introducing resultantflash reflux into` Contact with said vaporous mixture undergoingdephlegmation to assist the dephlegmation and to be supplied with saidcondensate to the secondmentioned cracking treatment, and condensing thevapors uncondensed by said dephlegmating steps.

JEAN DELATTRE SEGUY.

